For hydraulic systems in agricultural vehicles, such as, e.g., in agricultural haulers or tractors, but also in harvesting machines, as well as construction and forestry equipment, it is known to provide load-pressure-dependent supplies for the individual hydraulic loads. Such systems, also known as load-sensing systems, can be operated both with fixed displacement pumps and also with variable displacement pumps regulated by feed-volume flow. For the use of fixed displacement pumps, a load-pressure-dependent supply is realized in that a fixed feed-volume flow is discharged by means of a discharge line as a function of the load pressure. In contrast, variable displacement pumps can be operated directly as a function of load pressure. It is further known to supply the hydraulic load on the mentioned vehicles in a priority-controlled way, so that, if there is a hydraulic undersupply due to operation, hydraulic loads with a higher priority level are preferentially supplied hydraulically relative to hydraulic loads with a lower priority level. Thus, hydraulic loads, such as, e.g., a hydraulically operated steering mechanism or hydraulically operated braking mechanisms belong to a higher priority level than, for example, a hydraulically operated linkage to the vehicle. This can belong, in turn, to a similarly higher priority level relative to another hydraulic load, for example, a lifting mechanism located on the vehicle. Thus, several priority levels are often to be taken into consideration for the different hydraulic loads in a load-pressure-dependent hydraulic system.
In order to realize reliable priority control, priority valves in the form of pressure regulators are used in hydraulic load-sensing systems, with these valves controlling a priority scale for supplying individual hydraulic loads in the case of a hydraulic undersupply of the overall system. As a rule, the individual hydraulic loads are each connected to at least one control valve by means of which a supply of the feed-volume flow on the side of the hydraulic pump is controlled. In the supply of each control valve there is a priority valve that is closed by a load-pressure signal of a preferential hydraulic load and reduces or throttles the volume flow, in order to guarantee the hydraulic supply of the preferential valves. For example, for realizing two priority levels in the hydraulic systems or arrangements known in the prior art, one priority valve is used. For the realization of three priority levels, as mentioned above, typically two priority valves are thus needed. In the known systems it is therefore disadvantageous that these are constructed and designed for a specified number of priority levels with, for the most part, also a specified number of hydraulic loads, that is, they are relatively inflexible and can be expanded or adapted afterward only with much effort. For example, should a hydraulic system with two priority levels later be expanded to one with an additional priority level, or should an additional hydraulic load be added to an existing priority level, then this is usually associated with considerable structural expense and increased structural volume. If this is to be avoided, then the system must be limited to a few, e.g., two priority levels and the otherwise different, subordinate hydraulic loads must be combined into one priority level. However, for an undersupply of the overall system, this could lead to the result that one of the combined hydraulic loads does not receive a sufficient volume flow supply and thus fails. This is especially disadvantageous when it involves a hydraulic load that should have an actually higher supply priority relative to a hydraulic load combined in the same priority level.